Accurate characterization of deformation modulus of soils is essential for seismic hazard assessments and resilient geotechnical infrastructure design. Conventional techniques often yield discontinuous or biased modulus estimates due to sample disturbance and limited spatial coverage. For the first time, we introduce an in situ approach that exploits natural tidal forces coupled with distributed fiber‐optic sensing technology for continuous profiling of subsurface soil stiffness in a tidal river delta. Field measurements in the Yangtze Delta captured synchronous tidal‐induced pore pressure fluctuations and soil strain responses, demonstrating consistent linear stress–strain behavior from which depth‐resolved constrained moduli were derived. This tidal‐driven method effectively identifies subtle mechanical contrasts and meter‐scale interlayers with anomalously high or low stiffness, and enables continuous, long‐term monitoring of temporal and seasonal changes in soil stiffness. The proposed technique holds substantial promise for applications in sedimentological process studies and resilient infrastructure development within geologically dynamic coastal and deltaic environments.

Soil nailing has become a common method for improving slope stability due to its cost-effectiveness and easy installation. However, concerns have been arisen regarding the quality and integ...